Does it come with the certificate of athenticity or not?

No, we provide a 2 year warranty through Amazon

Is it a replica watch or authentic genuine swiss made tag heuer watch?

Dear Customer, Thank you for contacting us. We only sell brand new, 100% authentic products. All products ship in their original manufacturer’s packaging with seals and tags intact. We do not sell used or refurbished products and we do not accept any trade-ins. Please do not hesitate to call us for further assistance, we will be happy to help you. Kind regards, Millie.

Is the clasp the new or old version,

The "old" clasp vs. the "new" clasp: I've owned Tags for over 20 years... I honestly have not noticed a difference in the clasp and look of the clasp. Thus if this is a recent change in the last 12 months, then I do not know what the New one looks like and the Tag I purchased had the same clasp as all my other Tags. Could you or anyone explain when the new clasps were introduced and what the changes were. I hope I could in some small way. TGK